The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
18. On account of the scriptural statement of difference.
The prâna is everywhere spoken of as different from speech, &c. The passage, e.g. beginning with 'They said to speech' (Bri. Up. I, 3, 2), enumerates speech, &c., which were overwhelmed by the evil of the Asuras, concludes thereupon the section treating of speech, &c., and then specially mentions the mukhya prâna as overcoming the Asuras, in the paragraph beginning 'Then they said to the breath in the mouth.'--Other passages also referring to that difference may be quoted, so, for instance, 'He made mind, speech, and breath for himself (Bri. Up. I, 5, 3).--For this reason also the other prânas are different in being from the chief prâna--Another reason follows.